Atomic absorption spectroscopy is a very sensitive method for the quantitative analysis of a looked for element in a sample. A light source, e.g. a hollow cathode lamp, emits a light beam, which includes light with the line spectrum of a looked for element. The sample is atomized, i.e. an atomic vapor is formed, in which the elements of the sample are present in atomic state. The measuring light beam is directed through this atomic vapor. The absorption is measured, to which the measuring light beam is subjected in the atomic vapor. The concentration of the element looked for in the sample can be determined from this absorption after suitable calibration.
The atomization of the sample can occur by "electrothermal atomization". There, the liquid sample is introduced into a furnace. At first, the furnace is heated up to a drying temperature. The solvent vaporizes at this drying temperature. Subsequently a heating of the furnace up to a higher charring temperature occurs. Thereby, chemical compounds in the sample are split up. Also smoke can develop. Finally the furnace is heated up to an atomizing temperature, in which a "cloud of atoms" develops in the furnace, in which cloud of atoms the elements of the sample are present in atomic state. The measuring light beam is directed through this cloud of atoms.
Usually the furnace is a graphite tube. The electric current is passed through this graphite tube either through annular electrodes in longitudinal direction or through radial contact pieces in circumferencial direction. In order to protect the furnace made of graphite against the access of air and burning, at the high temperatures, the furnace is flown around inside and outside by an inert gas flow. This inert gas flow also carries away the vaporized solvent, during the drying process of the sample, and solid decomposition products, during the charring process.
It takes some time until the vaporized solvent and the decomposition products are carried away by the inert gas flow. Therefore, the drying and charring steps take undesirably long time. It is desired to shorten the time necessary for an analysis. Thereby, more analyses per hour can be made with one apparatus. Besides, the durability of a graphite furnace increases, if the graphite furnace is heated only for a short time for each analysis.
From European Published Patent Application No. 0,356,566 a method and a device are known for the electrothermal atomization of samples, in which device a sample liquid is vaporized by a "thermospray"-vaporizer and is guided into a graphite furnace as vapor jet. The graphite furnace is kept at a drying temperature. The sample condenses at the wall of the graphite furnace or a platform provided therein, while the vaporized solvent is sucked off by a vacuum. Thus the time for analyses can be shortened and the amount of the sample substance atomized with one analysis and thus the sensitivity can be increased. There, the graphite furnace is a longitudinally heated graphite tube, which is hold between annular contacts at its ends. The sucking-off of the solvent occurs through suction passages, which are formed in these contacts and are connected to a suction pump. There, a special arrangement with a thermospray-vaporizer is required.